1. Field of the Invention
This invention relates to scanners, particularly to the frame of a scanner or copying machine.
2. Brief Review of the Related Art
In a scanner, it is important to maintain a fixed light path from the scanned document to the light sensor. An approach to maintain the fixed light path is to use the Dual Light Module. In a conventional scanner, the scanning window and the light sensor are mounted on different component parts of the scanner frame. Between the scan window and the light sensor are many optical components. The interfaces between these components may have mechanical tolerances relative to one another. As a result, the light path may vary from the design value. Then, error may be introduced in the reproduced image.
FIG. 1 shows a prior art mounting structure of a dual optical module scanner as disclosed in Taiwan Patent Application No. 084210836. In this figure, a scanner window 12 is mounted on the frame 10 of the scanner through two L-shaped brackets 11. The sensor 18 is mounted on the bottom surface of the frame 10. The L-shaped brackets 11 have two flanges 114 to scanning glass 12. The bottom surfaces of the brackets 11 rest on two flanges 14 of the frame 10. A guiding rail 16 is mounted on the frame for one or two optical modules (not shown) to slide back and forth. The guiding rail 16 is hanging on the frame 10 through two holes 15 along the side wall 17 as shown in the 3-dimensional drawing FIG. 2. The L-shaped brackets 11 are pinned to the frame by pins 13 as shown in FIG. 1 through holes 103 on the flanges 14 as shown in FIG. 2.
The structure in FIGS. 1 and 2 have tolerance problems. The optical system has three optical sub-units. All these sub-units may have relative interface offset with respect to each other. If there is any offset due to tolerance in their dimensions, the length of the light path will be affected.
To avoid the tolerance problem, the light sensor 18 and the guiding rail 16 for the scanning carriage, the material of the frame 10 must be of low temperature coefficient metal. At present, the frame 10 is essentially made of sheet metal base, covered with the bracket 11, which improves the appearance and supports the heavy scanning glass window. The bracket also serves as an interface between the metal base and the glass window to avoid direct contact of the hard surface of the window and hard surface of the metal frame. As shown in FIG. 1, the L-shaped bracket supports the window at the interface (flange) 114. Such a structure suffers from the tolerance problem of the cushioning bracket.
An object of this invention is to avoid any light path error between the scan window and the light sensor. Another object of this invention is to planarize the surface of the scan window and top surface of the frame.
These object are achieved by planarizing the top surface of the scanner frame, where the light sensor is mounted, with one of the surfaces of the scan window. With the two coplanar surfaces, there can be no relative motion between the glass window and the frame and the light path between them cannot deviate. The light path between the scan window and the light sensor on the frame of the scanner does not vary regardless of any interface tolerance of the optical components of the optical modules.